This is the current version on airways 06/06/00

Read first the text book: Computed Tomography and Magnetic resonance of the Thorax by Nadich et all

Then go through this exercise to assess your comprehension

This lesson is on recognition of normal airways. You need to have a clear understanding of  Anatomy of bronchial tree especially three dimensional perspective. Recognition of airways by CXR, Bronchograms and CT will be reviewed.

Q: Describe extent and relationships of Trachea.

• Larynx (C6) to Carina (T5)

• Slight deviation to right

• Walls are parallel

• Aorta indents slightly on left, above carina

• Courses antero-posterior obliquely, hence the position will vary depending on the level of sections

• Progressive caudal sections will show trachea more posteriorly

• Lies anterior and slightly to right of Esophagus

• In contact with mediastinal pleural reflection of RUL (right Para tracheal stripe)

• Potential space between trachea and esophagus and is occupied by lungs (retro tracheal recess) (posterior tracheal band in lateral chest)

Q: Describe the appearance and dimensions of Trachea .

• Cartilaginous and membranous tube

• Walls are parallel

• Thin wall , well defined internally by air and externally by fat

• Smoothly serrated contour

• Horse shoe shaped cartilage rings at regular intervals

• Flat membranous part posteriorly

• Variations in shape and size common

• Cross sectional appearance varies from rounded, oval to horseshoe shaped with a flatter posterior wall

• Mean AP diameter 20 mm

• Mean Transverse diameter 17 mm

Q: What is the location and the mean angle of carina?

• At the level of T5 and louis angle of sternum, trachea (carina) divides into left and right main stem bronchi

• Mean carinal angle is 56 degrees

Q: What is the length diameter and direction of right maim bronchus ?

• More straight and in line with Trachea in adults, reason for aspiration being more common on right

• Symmetrical to left upto 15 years, reason why aspiration is equal on both sides at this age.

• Transverse diameter of right main bronchus is 15 mm 

•  2.2 cm long

Q: What is the length diameter and direction of left maim bronchus 

• Transverse diameter of left main bronchus is 13 mm 

•  5 cm long

Q: What is the origin, length, diameter,  direction and divisions of  right upper lobe bronchus?

• Arises from lateral aspect of right main bronchus

• 2.5 cm from carina

• Horizontal orientation

• Seen as round lucency on lateral (end on view)

• Divides into anterior, posterior and apical segments

• Anterior and posterior segments have horizontal orientation

• Apical segment has a vertical orientation

Q: What is the origin, length, diameter,  direction and divisions of right intermediate bronchus

• From RUL to RML and RLL

• 3-4 cms long

• Has a vertical orientation

Q: What is the origin, length, diameter,  direction and divisions of right middle lobe

• Arises from anterolateral aspect of intermediate bronchus

• Opposite the origin of superior segment of RLL

• Has a horizontal orientation

• Bifurcates into lateral and medial segments

  • Both of them have a horizontal orientation

Q: What is the origin, length, diameter,  direction and divisions of  right Lower lobe

• Superior segmental bronchus takes off opposite RML along the posterior aspect of RLL bronchus

• Superior segement has a horizontal orientation

• Medial basal segment takes off along medial side of RLL bronchus

• In AP projection basal segments are in the following order anterior lateral, posterior and medial  basal segments

• In lateral same relationship anterior - lateral - posterior (ALP)

• Oriented in

Q: What is the origin, length, diameter,  direction and divisions of left maim bronchus 

• Transverse diameter of left main bronchus is 13 mm 

•  5 cm long

• Oriented obliquely

Q: What is the origin, length, diameter,  direction and divisions of left upper division

• Divides into LUL  (upper division) and Lingula (lower division)

• Horizontal orientation

• LUL 

  • 1 cm long

  • Horizontal

  • Divides into apical-posterior and anterior segments

    • Apical-posterior segment has a vertical orientation

    • Anterior segemnt is oriented

• Lingula 

  • 2-3 cm long

  • Oblique course

  • Divides into superior and inferior segments

    • Segments are obliquely oriented

Q: What is the origin, length, diameter,  direction and divisions of left lower lobe

• Superior segment takes off posteriorly first

• Superior segment is oriented horizontally

• No separate medial basal segment

• LLL beyond superior segment is vertically oriented

• Same ALP relationship as right

• Medial basal segment arises with anterior basal segment (anteromedial basal segment)

Q; List the tracheal stripes, normal size and significance of abnormality.

• Right Para tracheal stripe width ranges from 1-4 mm

  • Width greater than 4 mm indicates disease

• Posterior tracheal band seen on lateral 

  • obliterated by cancer esophagus or disease of medial portion of RUL 

• Posterior wall of intermediate bronchus in line with trachea beyond RUL orifice

  • On left posterior wall of left main does not form a line because it is in contact with airless mediastinum and left pulmonary artery.

Q: What are the lucencies seen in lateral view over tracheal air column?

• Two circular translucencies in line with tracheal air column is RUL and LUL

Let us go through  concepts for recognition of airways by CT chest

Q: List Central airways

• Trachea

• Carina

• Main-stem bronchi

• Lobar

• Sub segmental bronchi

Q: Central airways are easily definable with  CT. How are they useful in reading the film?

• Bronchi are important sites for disease

• Provide road map into the lung parenchyma

• Point of orientation for interpretation of hilum (Bronchi serve as a lattice on which pulmonary arteries and veins drape)

 Ability to visualize Bronchial anatomy depends on

• Size

• Orientation

Q: List Bronchi with horizontal orientation

• RUL

• Anterior segment

• Posterior segment

• LUL

• Anterior segment

• Middle lobe

• Medial segment

• Lateral segment

• Superior segmental bronchus of Lower lobes

Q: Bronchi with vertical course (Circular lucencies)

• Apical segment of RUL

• Apical-posterior segment of LUL

• Bronchus intermedius

• Proximal portion of both lower lobes beyond superior segmental bronchus

Q: Bronchi with oblique course (difficult to visualize) (oval or elliptical in shape)

• Lingular bronchus

• Superior segment

• Inferior segment

• Lateral and medial segments of  middle lobe

Q: Is visualization of bronchi in the periphery normal?

Visualization of bronchi in the periphery of lung is abnormal suggesting thickening of wall or parenchymal disease

Now we are ready to review CT sections.

For easier review I am going to take you through right bronchial tree and left bronchial tree in sequence.

Q: What are the CT sections by whch you evaluate the right lung bronchial segmental anatomy

Five characteristic sections

• Distal trachea carina

• RUL bronchus

• Bronchus intermedius

• Middle lobe bronchus

• Lower lobe bronchus

Q: Click to look at the section at the level of Carina. Identify the labeled structures.

• Circular lucency( Apical segmental bronchus of RUL) in association with artery and vein

• Vertical course of apical segment of RUL

• RUL pulmonary artery. Artery lies just medial to bronchus

• Right superior pulmonary vein. Vein just lateral to bronchus

Q: You are looking at section at the level of RUL bronchus (at or just below carina).  Identify the labeled structures.

• RUL course horizontally

  • RUL bronchus originates more cephalad than LUL bronchus

  • Above the right main pulmonary artery

  • Posterior wall is in contact with either posterior segment of RUL or superior segment of RLL

• Proximal portions of anterior and posterior segments are visualized

• Origin of apical segment of upper lobe superimposed on the distal portion of RUL as rounded decreased density

• Truncus anterior first major branch of right pulmonary artery lies anterior to RUL bronchus

• Branch of right superior pulmonary vein lies at the angle between anterior and posterior segmental bronchi

• Anterior and medial to truncus anterior lies RUL vein (the apical-anterior vein)

Q: You are looking at section at the level of  bronchus intermedius.  Identify the labeled structures.

• Extends from RUL bronchus to RML bronchus

• Lies directly behind right main pulmonary artery

• Medial to right intralobar pulmonary artery

• Posterior wall in contact with superior segment of RLL

• Azygoesophageal recess is along posteromedially separated by lung tissue

• Inferior to bronchus right superior pulmonary vein lies alongside the lateral border of right interlobar pulmonary artery

• Multiple veins can be identified in this location

• Right main pulmonary artery at the lateral border of intermedius bronchus turns inferiorly and becomes interlobar pulmonary artery.

• At this position the artery may have a triangular configuration

Q: You are looking at section at the level of RML bronchus  Identify the labeled structures.

• Middle lobe bronchus origin also marks beginning of right lower lobe

• Extends anteriorly at a slightly oblique angle

• Divides into medial and lateral segments

• Since RML extends inferiorly the medial and lateral segments may be located in a lower plane

• Triangular spur at the site of bifurcation

• Superior segment of RLL arises at the same level as RML or at a slightly lower level

• Superior segment of RLL courses posteriorly and runs in a horizontal plane

• Interlobar pulmonary artery is vertical and lies immediately lateral to RML and RLL bronchi

• Artery has an oval configuration at this point

• Right superior pulmonary vein lies medial to RBL bronchus and can be seen entering the upper portion of left atrium

Q: You are looking at section at the levell of RLL basilar segments  Identify the labeled structures.

• Lower lobe beyond superior segment is vertical and is recognized as a circular lucency

• Lies medial and anterior to lower lobe pulmonary artery

• Appears suspended by superior portion of the inferior pulmonary ligament

• Medial basilar segment arises first, anterior to inferior pulmonary vein

• Anterior , lateral and posterior basilar bronchi course towards the anticipated positions

• Branches of right interlobar pulmonary artery are round and lay posterolateral to the proximal portions of basilar segments

• Inferior pulmonary veins are oriented horizontally and can be traced to right inferior pulmonary vein and subsequently into the lower portion of left atrium.

Q: What are the CT section by whch you evaluate the left lung bronchial segmental anatomy ?

• Lower trachea and carina

• Upper portion of LUL

• Lower portion of LUL

• Upper lobe spur

• LLL basilar segments

Q: You are looking at section at the level of lower trachea and carina. Identify the labeled structures.

• Apical-posterior segmental bronchus is separated from the left main bronchus by the left main pulmonary artery, which courses over LUL bronchus at this level

• LUL pulmonary artery cab be traced to its origin from the left main pulmonary artery and lies posterolateral to the left superior pulmonary vein

• apical-posterior segmental bronchus LUL  

  • Apical segment

  • Posterior segment

    • Seen as circular lucencies.

• Superior pulmonary vein tends to be located anteriorly

Q: Left upper lobe

• LUL bronchus originates lower than RUL bronchus

• Forms a sling over which the main pulmonary artery passes

• The LUL bronchus is large

Q: You are looking at section at the level of upper portion of LUL  Identify the labeled structures.

• Posterior wall is smooth and slightly concave caused by the left pulmonary artery

• The origin of the apical-posterior segmental bronchus can be recognized as area of increased lucency on the distal portion of LUL

• Superior segment of Lower lobe abuts the posterior portion 

• Posterior wall of LUL bronchus is slightly convex because it is indented superiorly and posteriorly by the left main pulmonary artery

  • Posterior to LUL bronchus the left pulmonary artery continues as interlobar pulmonary artery

  • Appears triangular at this level because of the change in course

• Left superior pulmonary vein lies in front of LUL bronchus and has a horizontal course

  • Distinct branching can be identified peripherally

Q: You are looking at section at the level of lower portion of LUL  Identify the labeled structures.

• Left upper lobe spur is the landmark Triangular in shape.

• Spur marks the origin of LLL (secondary carina)

• The lingular bronchus arises from the undersurface of the distal portion of LUL

• Courses obliquely inferiorly

• Can be recognized by increased radiolucency at the distal portion of LUL similar to apical-posterior segment

• Left interlobar artery has a vertical course and lies lateral to the spur

• Lateral to the origin of the lingular bronchus the pulmonary artery to lingula can be identified

• Directly anterior to LUL bronchus is the inferior portion of the left superior pulmonary vein

• Pulmonary parenchyma can be seen between pulmonary artery and descending aorta (retro bronchial stripe)

Q: Section below LUL bronchus

• Lingular bronchus is oval or elliptical  separated spatially from LLL bronchus

• Superior and inferior segments originate at a considerable distance from origin of lingular bronchus and often not recognized

Anterior segment of LUL is the only segment coursing anteriorly in a horizontal plane

Highly variable in origin from LUL

Q: You are looking at section at the level of LLL basilar segments  Identify the labeled structures.

• Same as right

• Superior segment of LUL is similar to right side

• Proximal portion of LLL below the superior segment is suspended by the inferior pulmonary ligament

• Basal segments of LLL are similar to right side

• Medial and anterior basal segments arise as a common trunk

• Branches of pulmonary artery to the lower lobe lie lateral and posterior to the basilar bronchi

• Left inferior pulmonary vein is horizontal and cab traced to left atrium

• Left inferior pulmonary vein course along the lateral border of descending aorta

The session is over

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